The present invention relates to a binocular or other optical viewing instrument which is designed specifically for users who are wearing eyeglasses.
Traditionally, binoculars and other optical viewing instruments have been designed for non-eyeglass-wearing users. This has meant that the typical eye relief (the distance between the exit lens and the eyeball at which full field of view is achieved) has been designed to be approximately ten to twelve millimeters. When a user wearing eyeglasses or protective lenses attempts to use such an instrument, the eyeglass lens is necessarily superimposed between the viewer's eye and the exit lens of the optical instrument. This means that the eye relief distance of ten to twelve millimeters falls significantly short of the user's eye and the user's field of view is accordingly considerably reduced.
Previous attempts to adapt binoculars and other optical instruments for use by eyeglass wearers have proven to be inadequate compromises. One approach has been to place flexible eyecaps or eye pieces on the viewing end of the ocular tube or tubes of the instrument. These eyecaps have usually been made of a flexible material such as rubber or the like and designed to conform to a first extended condition for use by a non-eyeglass-wearing user, but which can be folded over to significantly reduce the axial length of the eyecap for use by an eyeglass-wearing user. While this approach significantly improved viewing conditions for eyeglass wearers, several problems remain. The repeated folding and unfolding of the resilient eyecaps has tended to stress and distort the material. Rubber or similar materials have tended to become brittle and cracked. This not only reduces the flexibility of the eyecap, but also can mar or scratch the eyeglass lenses. Furthermore, as the resilient material loses its elasticity, the axial length of the eyecap in both positions tends to change.
Another approach has been to provide an eyecap or eye piece which is telescopically mounted on the viewing end of the ocular tube of the instrument, but which is movable axially relative thereto so that the axial length of the eyecap is adjustable. Such eyecaps have used threaded mounts for adjustment or incorporated springs which urge the eyecap to normal extended axial length for use by a non-eyeglass wearer, but which can be compressed to reduce the axial length of the eyecap for an eyeglass-wearing user. In both instances, these mechanisms have tended to increase the weight and complexity of the optical instruments, and therefore the cost and difficulty of manufacture. In the case of the spring-mount, the requirement for an eyeglass user to place a constant force against the spring-urged eyecap has significantly increased the fatigue level of an eyeglass-wearing user. In the case of either the folding rubber eyecap or the spring-loaded, axially adjustable eyecap, if a user is jostled or merely lowers his arms to rest for a moment, the axial length of the eyecap can change, necessitating constant adjustment and resultant frustration and fatigue.
As previously mentioned, these approaches have represented compromises at best, and have failed to address the fundamental problem that typical binoculars or other optical viewing instruments are designed with an eye relief intended for the non-eyeglass wearer. It is clear, then, that a need exists for a binocular or other optical instrument which is designed specifically for optimal viewing by eyeglass-wearing users. It is also clear that such an instrument should be mechanically simple and should be capable of manufacture by readily available production techniques.